I researched a lot about this feature and there is not even one file manager in Android that can do PDF thumbnail or Word thumbnail. So your Total Commander application can have large advantages compare to those other Android file managers (even how popular they are). I can support with everything I can, because i desperately need it, and many other people will do the same too.

It is very good for Total Commander Android app future, for example, you can check on Google with keyword: "android MS word thumbnails" . There is not a solution for it, also this post is already in first page of Google search for many keywords (good for SEO) (even the above keyword) and many of people research about it now and in the future can know and use Total Commander.

itextpdf is under GPL (even the stronger AGPL), so it's a no-go. I would have to publish the source of Total Commander, which I prefer not to do, because it is often abused by malware makers bringing out their own copy of TC.